From the Clinical Pharmacology Unit (K.M.M.-P., A.D.B., S.M.L.W., Y., C.M.M., I.B.W.) and Department of Clinical Medicine (F.C.H., A.F.), University of Cambridge; Department of Radiology (P.W.P.B., S.H.), Addenbrooke’s Hospital; and Trinity College (J.B.), University of Cambridge, Cambridge, United Kingdom. (At 2006-09-12)